A minimax calculation by a minimax (mini-MAX) method is used particularly in an action deciding problem of deciding an action to take, and is based on the minimax loss criterion in which an action minimizing the maximum loss in possible states or an action maximizing the minimum ensured benefit in possible states is decided as an action to be taken for an uncertain future state. The minimax calculation is used not only for action deciding problems based on the minimax loss criterion but also for various industrial purposes. For example, if a grade (degree of conformance to true) of each term on the left side of Fuzzy logic expressions (a set of expressions in the form of “if A and B then X”) is given in relation to Fuzzy control of a home electrical appliance or a vehicle, the minimum value thereof is defined as a grade value on the right side to obtain the maximum value on the right side in a disclosed technique. For example, refer to Japanese Patent No. 2633161.
In an action deciding problem based on the minimax loss criterion, a set of maximum evaluation values V1max, . . . Vjmax, . . . Vmmax, each of which corresponds a maximum value among the evaluation values indicating losses when taking a specific action Bj in possible states A1 to An, should be obtained for each action Bj among actions B1 to Bm in order to determine the action that minimizes that maximum evaluation value. Accordingly, m×n evaluation values must be obtained.
However, even if the conventional technique described above is applied, m×n evaluation values must be obtained in the action deciding problem, causing a problem that a large amount of time is required for finding a solution to the action deciding problem.